The present invention relates generally to an automatic choke mechanism for an internal combustion engine, and more particularly to an automatic choke unit which is effective in overcoming exhaust gas pollution problems without adversely affecting stable engine operation during idling or while cruising at a low speed before the engine is sufficiently warmed up.
When an internal combustion engine is cold, insufficient vaporization of fuel is compensated by enriching the fuel-air mixture during the warming-up operation of the engine. The optimum air-fuel ratio which should be provided may vary depending upon changing operating conditions of the engine such as might occur when the engine is operated during starting, idling, cruising at a constant speed, acceleration and the like. An optimum ratio will also be dependent upon surrounding temperature levels and operation of the engine during its warm-up stages. Automatic choke valves have been heretofore used in order to obtain an optimum air-fuel ratio for an engine under various changing operating conditions.
Recently, various improvements have been made in automatic choke systems in order to decrease the time required during warm-up so that operation of the choke valve is required to a lesser extent. As a result, when during the operation of the vehicle the engine has been warmed up to some extent, operation of the choke valve is not required and the choke valve may be opened immediately thereafter.
Conventional automatic choke valves are usually operated by a bimetallic spring member or the like which is responsive to temperatures of the exhaust gases, engine cooling water or an electric heater. Accordingly, it is likely that sufficient engine heat to rapidly open the choke valve may not be obtained. As a result, harmful pollutants such as CO and HC will be discharged from the engine for a relatively long period of time.
In order to overcome these problems, there has been proposed a choke opener mechanism which is adapted for use with an internal combustion engine having improved warming-up characteristics. As in the case of conventional automatic choke valves, the opening of the choke valve is controlled by a diaphragm mechanism which is, in turn, controlled in response to the vacuum of the intake manifold of the engine. The intake manifold pressure changes in response to engine temperature and vehicle speed and, accordingly, a rich fuel-air mixture may be supplied. However, when the vehicle is running after the engine has been warmed up to some extent, the choke valve will be forced to the fully opened position.
Conventional carburetors are usually provided with a fast idle mechanism of the type which cause opening of the throttle valve to an excess degree in response to a small opening of the choke valve so that stable idling may be ensured when the engine has not as yet been sufficiently warmed-up. However, when the choke valve is forced to the fully open position while the vehicle is running, the fast idle mechanism is deactivated before the engine is sufficiently warmed up thereby resulting in unstable engine idling and stalling. Thus, engine operation will be adversely affected.
The present invention is directed to provision of an automatic choke valve having a choke opener mechanism of the type which permits operation of the fast idle mechanism even after the choke opener mechanism has been actuated. In the operation of the present invention, the choke valve may be forcibly opened to a position short of the fully opened position when vehicle speed and engine temperature reach predetermined levels with the choke valve being thereafter moved to the fully opened position by the normal operation of a bimetallic spring member after the engine has been sufficiently warmed-up.